The focus of this project is to improve the diagnosis and treatment of fetal disease. Focus is placed on the prenatal diagnosis of congenital anomalies with non-invasive methods (e.g., high resolution ultrasound and color Doppler flow mapping) and invasive methods. The Branch pioneered the utilization of thin-gauge endoscopy in the differential diagnosis of fetal obstructive uropathy. Fetuses with sonographic findings of lower obstructive uropathy are a diagnostic and therapeutic challenge. Ultrasound imaging alone cannot establish the cause of the obstruction and treatment with percutaneous vesicoamniotic- shunts has a complication rate of 25%. We inserted a fiberoptic endoscope through the lumen of the needle (or trocar) placed into the fetal bladder and visualized the bladder neck and ureteral orifices. Eleven fetal cystoscopies were performed successfully. Ureteral webs were noted in two fetuses. A catheter was passed from the fetal bladder into the amniotic cavity in two cases to treat the obstruction. Ureteral probing with a flexible catheter was sufficient to treat the obstruction in other cases. This impressive technological achievement is a landmark in fetal medicine and surgery. High resolution ultrasound was used to establish the prenatal diagnosis of congenital anomalies in the cardiovascular system. Color Doppler flow mapping has improved the accuracy of prenatal diagnosis of several other conditions which could only be suspected by gray-scale sonography. During the past year, the investigators of the Branch reported the first diagnosis of agenesis of the right and left portal veins. The Branch also described a diagnostic approach for the identification of coarctation of the aorta with the aid of color-flow Doppler ultrasound. Color flow mapping studies of the fetal circulation allowed the identification of fetuses with reversal of blood flow in the ductus venosus. The prevalence of this condition was 2.4% and perinatal death occurred in all 5 fetuses with reversal of diastolic flow in the ductus venosus. The hemodynamic mechanisms responsible for reversal of flow appeared to increase pressure in the left atrium and diastolic heart failure.